FAQ & Common Terms

Discussion in 'General Topics' started by dslmaster, Oct 13, 2004.


  1. dslmaster

    dslmaster Administrator Staff Member




    Digital Subscriber Line or DSL - refers to the broadband access technology that uses existing copper infrastructure to deliver data, voice and video simultaneously.

    DSL can deliver high-speed data, voice and integrated services over traditional twisted-pair copper wire that is already available in many business and residential locations. Aside from increasing the speed, DSL offers the flexibility and reach required for businesses to extend on-line resources and applications to remote sites for teleworking.

    SDSL (Symmetric DSL) - this is a type of DSL access where the downstream speed is the same as the upstream speed. This type of access does not support voice connections on the same line. This symmetry is particularly beneficial to businesses that would like to be able to send as fast as they can receive. Some of the commom applications are:

    * Internet Browsing
    * File downloads from the Internet
    * Sending and receiving of emails
    * Multimedia Web Hosting (voice, video)

    ADSL (Asymetric DSL) - ADSL delivers high-speed data and voice service over the same line. The key to ADSL is that the upstream and downstream bandwidth is asymetric, or uneven. In practice, the bandwith from the provider to the user (downstream) will be the higher speed path.

    IDSL (ISDN DSL) - This type of access is a hybrid of ISDN and DSL. It is an always-on alternative to dial-up IDSN. Similar to IDSL, it does not support voice connections on the same line.
     
  2. dslmaster

    dslmaster Administrator Staff Member




    1. What is xDSL?
    xDSL is a generic abbreviation for the many flavors of DSL or Digital Subscriber Line technology. xDSL refers to the technology used between a customer's premises and the telephone company, enabling more bandwidth over the already installed copper cabling that users traditionally had.

    There are several variations of xDSL that include:
    ADSL - Asymmetric Digital Subscriber Line
    HDSL - High Bit-Rate Digital Subscriber Line
    VDSL - Very High Bit-Rate Digital Subscriber Line
    SDSL - Symmetric Digital Subscriber Line

    2. How does "xDSL" work?
    xDSL utilizes more of the bandwidth on copper phone lines than what is currently used for plain old telephone service (POTS). By utilizing frequencies above the telephone bandwidth (300Hz ~ 3,400Hz), xDSL can encode more data to achieve higher data rates than would otherwise be possible in the restricted frequency range of a POTS network. In order to utilize the frequencies above the voice audio spectrum, xDSL equipment must be installed on both ends and the copper wire in between must be able to sustain the higher frequencies for the entire route. This means that bandwidth limiting devices such as loading coils or Bridge tap must be removed or avoided.

    3. What Is ADSL?
    Asymmetric Digital Subscriber Line (ADSL) takes its name from the comparatively high bandwidth downstream, with low bandwidth upstream. ADSL can achieve data transmission at speeds 8Mbps over a single copper pair specifying loops up to 18,000ft at a wire thickness of 0.5mm and 0.4mm (24 Gauge & 26 Gauge).

    4. What Is The Difference Between 22, 24, 26 and 28 American Wire Gauge?
    AWG (American Wire Gauge) is a US standard set of non-ferrous wire conductor sizes. The "Gauge" means the diameter of the wire which commonly measured in Millimeter.

    Telephone wire is usually 22, 24, 26 or 28 AWG. The higher the number, the thinner the wire. Thicker wire can carry more current and will have less electrical resistance over a given length. Thicker wire is better for longer distances. For this reason, if extended distance was critical as a result of attenuation and crosstalk, a company installing a network might prefer telephone wire with the thicker gauge of AWG 24 to AWG 26.

    AWG - Metric Size(mm) - Loop Resistance(Ohms/Mile)
    28 - 0.32 - 685
    26 - 0.40 - 441
    24 - 0.50 - 277
    22 - 0.63 - 174


    5. Why is ADSL faster in some other countries ?
    Technically, ADSL can run at data speed of up to 8Mbps, but that rate is effected considerably by line length ( The further you are from the exchange, the less speed you can get ) from a copper pair. If you are very close to the exchange ( <1Km ) then you could run the line at 8Mbps downstream.

    6. DSL modems aren't really modems, are they?
    No, they're not. People call them DSL "Modems" because the term describes the gear in ways people understand today. Actually, the DSL equipment is a network termination device with a micro-router inside. It doesn't really make calls the way a traditional modem does. Nor can it be used to place calls to a traditional modem.

    7. Will I have to get a new phone number?
    No, your phone number will remain unchanged.

    8. What happens if the power goes out at my location? Will I lose telephone service if the power is cut to the DSL equipment?
    Your phone service will still work even if you completely disconnect all your DSL gear from the system. Power outages and failed DSL gear do not affect voice phone service. (Of course, if there are problems with the phone line, the DSL will probably have problems as well.)

    9. Can I set up the ADSL modem myself?
    It is not difficult to set up the ADSL modem yourself. Please refer to the Setup CD-ROM and User's Manual with the modem.

    10. What is involved in installing the ADSL?
    Modem installation means hooking up the equipment at your premises, which you can do yourself.
    Connecting the splitter to a wall jack, then to your ADSL modem and to your computer using cables. Then set up your computer for network access.
    If you require a new wall jack at your premises, please consult the telephone service company.

    11. Fixed or Dynamic IP ?
    This is mainly relevant for internet service providers. Your computer has an IP address when connected to the internet. When you use a modem and dial up, you are provided with an IP address. This IP is normally dynamic which means it changed each time.

    The same can be true of ADSL. There is a log in procedure, and you are then connected. You can then stay connected forever if you want.

    If your ISP provides a fixed IP address then you can run servers on your machine, and people can access it. This means you can have email actively delivered instead of collected periodically by POP3. You can run web and games servers. Generally it is a much better service.

    If you have dynamic IP then your address changes. This makes it much harder for people to get hold of you unless then know your IP address. You cannot easily have a name for your machine ( or web site or email ) as this would have to be updated every time you change your IP address.

    A corporate network can set up their own private fixed addressing for a wide area network.

    12. How are IP addresses assigned?
    With a router-type modem: A global IP address is assigned dynamically to the WAN side of the ADSL modem with a point-to-point protocol ( PPP ) connection. For PCs on a LAN, private IP addresses can be assigned, and the PCs access the Internet using network address translation ( NAT ).
    For the PCI/USB type ADSL modem, you use the Windows dial-up function to establish a PPP connection, and a global IP address would be assigned.
    A static IP addressing service may also be available, depending on the Internet service provider.

    13. Is a static IP address service available?
    It depends on the Internet service provider.

    14. I would like to set up a server using a global IP address. Is that possible?
    It depends on the Internet service provider. Please choose a service where you can be assigned a fixed global IP address. Check the ISP's service options to find out whether this type of service is available.

    15. NAT and no NAT ?
    NAT terms for Network Address Translation. For the Ethernet connected ADSL service, the line can be provided with a single IP address ( Fixed or Dynamic) and a block of private addresses or it can be provided with a block of fixed IP addresses.

    With a single address there are no incoming connections allowed. Only replied to outgoing connections using NAT can be received. However, with your own router you could configure port forwarding of certain ports to certain internal machines if you like.

    With a block of addresses the connection is an unfiltered connection, normally to the internet. The ISP could provide NAT or filtering at their end if they wish.

    All of this is in your control if you have your own equipment.

    16. Will I have a static IP address?
    In most cases, Basically, client-side DSL has IP addresses assigned using Dynamic Host Configuration Protocol (DHCP). With DHCP, IP addresses are assigned out of a pool of available addresses. Thus you may get a different IP address every time you connect.

    For most people, this is the preferred approach, because it is invisible to you and requires no special set-up on your side.

    However, in a few cases people or companies might require a static IP address. In those cases, server-enabled DSL will be required.

    17 . Can I use my own domain name?
    Conditions of service, including user domain names and the availability of e-mail services and hosting services, are at the discretion of each ISP and may vary.
    Please ask the service providers before you sign up.

    18. How is the authentication ID set for PPP connection?
    For USB/PCI ADSL Modem, you use the Windows dial-up function to establish a PPP connection, and the PC obtains the DNS information.

    19. How is DNS information set?
    For USB/PCI ADSL Modem, you use the Windows dial-up function to establish a PPP connection, and the PC obtains the DNS information.

    20. Does "Always-on" access mean that my computer is vulnerable to hacker attacks?
    We cannot tell whether the data communications that customers have with people outside their network constitute an attack in any particular instance.
    You will need to make your own security arrangements.

    21. Will I need a free IRQ to install the PCI ADSL Modem?
    Yes, you'll need a free IRQ.

    22. Can I take my ADSL service with me if I move premises?
    This depends on whether the premises that you are moving into belongs to an ADSL enabled exchange

    23. What is involved in an ADSL service qualification check?
    There are many requirements to be met before an ADSL service can be provided. Not all telephone services belonging to an ADSL covered exchange can necessarily have an ADSL service.

    A service qualification check will test whether your telephone line will meet the following requirements:

    Your telephone line belongs to an ADSL enabled exchange.

    Your home or business is within a certain distance from the CO.

    Your telephone line is a straight PSTN service without any ADSL incompatible equipment such as PABX.

    24. Does computer performance affect the access speed?
    Computer performance affects how fast received data can be processed. So this can make a difference to access speeds in environments that are otherwise identical.

    25. Are there any types of equipment that won't work with ADSL?
    You cannot use ADSL if you have a PBX or key telephone system. ADSL signals cannot travel through these systems. To use ADSL, you will need to have your telephone system rewired to bypass such equipment to avoid interferes with the high frequency spectrum used by ADSL.

    ADSL is not possible if you have a multiple phones on a single line. ADSL signals cannot go through these systems.

    26. What's a DSLAM ?
    The DSLAM is a Digital Subscriber Line Access Multiplexer. It's the box that your ADSL line terminates in at the Central Office. It takes the ADSL lines and combines their traffic to send it across the Central Office¡¦s network.

    27. What is a Microfilter or Splitter ?
    When you have your ADSL line installed, your existing analogue telephone service continue to work, and you can make voice calls as normal, with the ADSL Modem operating at the same time. The ADSL Data signal and the regular Voice signal are carried down the same line, each operating in a different part of the spectrum.

    In order that the ADSL data signal does not interfere with your regular telephones, fax machines and answering machine, you will need to fit a Microfilter or Splitter, The Microfilter or Splitter Strips Out the data signal so that your phones receive the normal voice signal without interference.

    28. What does a POTS splitter do and when do I need one?
    A POTS splitter uses a low pass filter to separate the low end frequencies of the telephone audio spectrum from the higher frequencies of the xDSL signals. The splitter should be a passive device, not requiring power so that voice service can be provided as has been in the past. This splitter allows for the traditional voice service that consumers are accustomed to. A splitter is required at both the customer premises and at the far end ( CO ).

    29. We have wall jacks in several rooms. Where should I put the splitter?
    Connect the splitter to the wall jack closest to the cable entry of your premises.
    Branch the telephone cable from the splitter's PHONE connector, and connect the separate cables to each room.
    In the event of noise on the line, you may be able to eliminate the noise by attaching a splitter and telephone to each wall jack.

    30. How do I tune my xDSL line for maximum performance?
    There is little you can do to really tune your DSL line. You're generally relying on the cabling plant installed in your house all the way through to the provider's network and your speed is typically determined at provisioning time.

    31. Can I have more than one xDSL line in my home?
    Yes, generally this is not a problem. The telephone company will provide as many lines, each on a separate copper pair into your house as you want.

    32. Is xDSL available in my area?
    To find out, you can check a number of sources.
    A. You can check with your local telephone company to see if they are providing xDSL services.
    B. Check around with your local Internet Service Providers (ISPs).
    C. Try the competitive local exchange companies (CLECs) in your area.
    D. There are some sites which claim to tell you if DSL is available in your area simply by filling in a online form.
    Unfortunately you cannot rely upon these sites for 100% accuracy. Even if you're told xDSL is available in your area, you still might be not able to get it. Often providers will need to perform a ¡§Qualification test¡¨ to determine if they can send and receive a signal within their parameters. Long local loops and poor cabling plants are common reasons for failing a loop qualification test.

    33. Can I use my 56K modem with my ADSL line?
    Theoretically yes. However, most ADSL providers have been installing separate ADSL circuits to the remote user without using a splitter to separate out the voiceband bandwidth. If a splitter was used, you could use a traditional POTS modem over the voiceband frequency spectrum of your phone line as you always did. In most cases however, the line is dedicated for ADSL Modem only.

    34. How do I determine how far I am from my CO?
    You can call your service provider and ask them for the address of your local CO and get an approximate distance from your residence to the CO.

    35. What are loading coils?
    Loading coils are used to extend the range of a local loop for voice grade
    communications. They are inductors added in series with the phone line which
    compensate for the parallel capacitance of the line. They benefit the frequencies in the
    high end of the voice spectrum at the expense of the frequencies above 3600Hz.

    36. What is a bridge tap?
    A bridge tap is a length of wire pair that is connected to a loop at one end and is unterminated at the other end. The reflection of signals from the unterminated bridge taps results in signal loss and distortion. It is generally harmful to ADSL connections and should be removed.

    37. What is the local loop?
    The last segment of the carrier network. The local loop extends from a telephone
    company¡¦s Central Office (CO) to an end user¡¦s residence, and is still primarily used for analog connections.

    This loop provides a user with access to the global telecommunications infrastructure that is installed all over the world. The local loop has been historically designed to provide voice grade audio service.

    38. What is the effect of noise?
    Noise may be defined as the combination of unwanted interfering signal sources whether it comes from crosstalk, radio frequency interference, distortion, or random signals created by thermal energy.
    The maximum data rate of a modem is limited by the available frequency range (bandwidth) and signal-to-noise ratio (SNR).
    On a communications channel, extraneous signals that degrade the quality or performance of the link.

    39. What is crosstalk?
    Crosstalk refers to the interference between channels. In the ADSL world, the interference between nearby cables can have a negative impact on the performance of the affected cables.

    Near-end crosstalk ( NEXT ) is a major impairment for systems that share the same frequency band for upstream and downstream transmission. NEXT noise is seen by the receiver located at the same end of the cable as the transmitter that is the noise source.

    Far-end crosstalk (FEXT) is the noise detected by the receiver located at the end of the cable from the transmitter that is the noise source. FEXT is less severe than NEXT because the FEXT noise is attenuated by traversing the full length of the cable.

    40. What is attenuation?
    Attenuation is signal loss due to the diminishing availability of signal energy, or signal power. As a analog or digital signal traverses across a medium, it fades. High attenuation may lead to the inability to recover the signal on the far end.

    Baseband transmission is extremely limited to attenuation.


    41. What is modulation?
    Modulation is a prescribed method of encoding digital (or analog) signals onto a waveform (the carrier signal). Once encoded, the original signal may be recovered by an inverse process called demodulation. Modulation is performed to adapt the signal to a different frequency range than that of the original signal.


    42. What are the monthly charges and changeover fee for switching from the 1.5Mbps service to the 8Mbps service?
    Each Internet Service Provider will announce its customer pricing schedule when it launches an 8Mbps service. Details please check with the local ISP.

    43. Do I need to protect my equipment against lightning?
    When lightning strikes, the current from the lightning can travel through the telephone cables, power cables, or Ethernet cables, damaging your ADSL modem or other peripherals. To protect your equipment from a lightning strike during a lightning storm or if there is any risk of lightning, we recommend that you remove the modular telephone cables attached to your ADSL modem and splitter. A variety of lightning protectors are available commercially. As some products may affect ADSL transmission quality, consult the retailer or manufacturer when you make your purchase.
     
  3. zackxxx

    zackxxx Member




    salamat po master.
     



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